This invention relates to short circuit protection of regulated power supplies, and more particularly to protection of power supplies having series pass transistors controlled by sense amplifiers to maintain constant load voltage.
The most common method of short circuit protection has been to sense the current drawn by the regulator load. When the current becomes excessive, the resulting voltage drop across the sensing element activates a protection circuit which in turn limits the current to a designed maximum. The disadvantages are that (1) the pass transistor is at maximum disipation under short circuit conditions, (2) the load regulation characteristics are greatly degraded, and (3) the regulator circuitry is active under short circuit conditions.
Another technique is to sense the output voltage of a regulator. When the output voltage falls, due to a short circuit, the lack of voltage activates a shut-down circuit. This control inhibits the regulator by removing input power. The regulator circuit remains inhibited until the input voltage is removed and reapplied to the protection circuitry. The disadvantages are that the circuit complexity and component count is greatly increased, and manual restart is normally required.